JPS61267934A - Manufacture of high-density magnetic recording medium and composition and suspension used therefor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION In recent years, tape recorders for live music, oral recordings, and video signals of movies and television broadcasts have proliferated. This is further exacerbated by the fact that computers and word processors require software in the form of floppy disks or hard disks. These are usually manufactured from suspensions of magnetic materials. To achieve good suspension of the magnetic particles, conventional methods dispense the dispersion onto the disk to form a thin coating. The coated disk is placed in a magnetic field while the coating is wet to orient the magnetic particles. The disk is then cured, usually through a recuperative thermal cycle. The yield with this method was very low.

It has previously been proposed that magnetic materials, such as fine ferric oxide particles, can be suspended in water and electrophoretically deposited onto a multilayer tape. The inventors have found that other liquid carriers with low dielectric constants and high resistivities, particularly the Isopars (15OPAR), are excellent materials for this purpose.

Toner particles must be charged with the correct polarity for electrophoresis to occur. This is the role of the charge directing agent. The liquid toner bath consisting of Imphal, toner particles, and charge directing agent must be electrically neutral.

That is, the charge directing agent not only introduces charge into the toner particles, but also creates particles with an equal number of opposite charges (called counterions). Counterions can be loaded individual molecular ions, chain polymers, micelles, or other molecular aggregates. There are two possible ways in which a charge directing agent can perform its function.

In the first method, the charge directing agent is neutral until mixed with the toner particles. When mixed, the enthalpy difference between the charge directing agent and the toner particles induces a chemical reaction such that the toner takes on a charge of one sign and the charge directing agent takes on a charge of the other sign. This is believed to occur due to the exchange of electrons between the two particles or due to the transfer of ionic molecular groups from the charge director molecules to the toner particles.

A second, more common way in which the charge directing agent functions is in the form of an ionic solution in a liquid carrier prior to mixing with the toner particles. When the toner and charge directing agent are mixed, one of the ionic species preferentially attaches to the toner particles. The sign of the ions deposited on the toner generally varies depending on the nature of the surface of the toner particles and the ionic species within the charge directing agent. A charge directing agent may positively charge one toner, negatively charge another toner, or not charge at all. A preferred strategy is for the larger of the two ionic species to adhere to the toner, and therefore the smaller, more mobile one to serve as the counter ion.

If the toner suspension is poorly charge-directed, i.e., the probability of ion deposition is low, so that on average fewer than one charge-directing agent ion (of the correct sign) is deposited per toner particle, the toner The particles tend to form flocs. The mechanism by which flocculation occurs is that neutral toner particles adjacent to charged toner particles have an induced dipole, creating an attractive force that binds the particles.

All toner particles in the bath will reach the same equilibrium chemical potential. At equilibrium, the charge on a particle increases as its radius increases (because its capacitance is inversely proportional to radius) and as the number of sites (called "hooks") on its surface to which charge-directing agent ions attach increases. The more, the bigger.

The viscous drag on a particle in a liquid is also proportional to its radius. Therefore, mobility (which is proportional to the charge on a particle and inversely proportional to viscous drag) tends to be independent of particle size if the density of surface hooks is the same on all particles. This means that if the hook density of the particles is unregulated, the particles will respond differently to the electric field and non-uniform deposition of toner will likely occur. As a result, the toner particles with the highest mobility will escape from the developer solution first, leaving the slower particles behind. As this progresses, even if the toner particle density is kept constant by replenishing the bath, the deposited density of the particles will decrease upon subsequent application of the developing dispersion, and the dispersion will become
It is said that it is exhausted.

If the toner suspension is too charge-directed, second, if it is an ionic solution, there will be extra ions of the same sign as the toner particles in the bath. This is referred to in the industry as a condition in which the toner has "continuous phase conductivity." When continuous phase conductivity is present, ions of the same sign as the toner particles compete with the toner particles to reach the imaging area.

As a result, the density of toner reaching the charged substrate is less than the optimum density. Continuous phase conductivity also adversely affects the efficiency with which toner is transferred from the initially deposited surface to the carrier in printing applications.

The inventors have discovered that substantially homogeneous films of ferromagnetic particles, such as ferric oxide, can be produced by encapsulating them in thermoplastic resins. The resin must be insoluble in liquid dispersants such as Imphal (trademark for a series of low boiling isomerized aliphatic hydrocarbon liquids manufactured by Exxon). Furthermore, the coating or encapsulant must melt after deposition to produce a smooth surface and to allow orientation of the ferromagnetic particles. Furthermore, the surface of the encapsulant must have multiple functional sites to accept the charge directing agent. This allows the production of tunably charged and equally mobile encapsulated ferromagnetic particles, such as ferric oxide. Thus,
The electric field applied to cause electrophoresis moves the electrophoretically mobile toner particles into place without depleting the suspension. The relationship between the encapsulant and the charge directing agent can be thought of as analogous to an ion exchange or acid-base phenomenon.

The present invention allows ferromagnetic materials to be used on tapes, floppy disks, etc.
The present invention relates to a method for producing high-density recording media by electrophoretically depositing onto hard disks, square plastic security cards, etc., and compositions useful in carrying out the method.

Japanese Patent Publication No. 50-28093 discloses electrodeposition of a paint obtained by emulsifying a resin together with a magnetic pigment in water. This paint is applied electrophoretically onto an aluminum disk. Emulsion liquid: 40 parts by weight of oxidizable acrylic resin, 4 parts by weight of water-soluble melamine resin, 1 part by weight of gamma ferric oxide
60 parts by weight, 10 parts by weight of isopropanol, 7 parts by weight of triisopropanol amine, and 279 parts by weight of ion-exchanged water
Consists of weight parts.

Japanese Patent Publication No. 52-25321 uses a composition similar to the above except that the emulsion contains an organic solvent that helps emulsify the water-soluble acrylic acid polymer. Methyl isobutyl ketone is mentioned as a preferred example.

Generally, according to the invention, magnetic pigment particles and a binder such as a wax, waxy polymer or polymer mixture are dry encapsulated together with auxiliary agents to create a significant number of functional sites, such as charge directing agents. The encapsulation must be such that the encapsulated pigment remains undamaged even under the harsh conditions of encapsulation and wet milling. The encapsulant must be insoluble in the dispersion medium. Encapsulation is accomplished by dry milling the encapsulating wax or waxy polymer mixture and the composition for creating the functional sites. The dry milled material is then wet milled with Inverru G1 Isopar H, Inverloo Lt Take Isopar-M in a mill. Wet milling of the finely ground primary dry dispersion produces a uniformly encapsulated pigment dispersion. Additional or different charge directing agents may be added during the dilution step. The charge directing agent uniformly imparts the desired polarity to the coated toner particles by chemically bonding to the functional sites or hooks of the particles. The uniformity of the coating masks the non-uniform nature of the magnetic pigment and prevents toner depletion characteristic of conventional liquid dispersions.

One of the objects of the present invention is to provide a method for producing magnetic recording media by electrophoretic deposition, in which the thickness of the deposited layer can be better controlled.

Another object of the present invention is to provide a method for manufacturing a magnetic recording medium with uniform thickness and no pinholes.

It is a further object of the present invention to provide a method for rapid and continuous mass production of magnetic recording media.

It is further an object of the invention to provide a suspension of encapsulated acicular ferromagnetic particles that does not break during the encapsulation and milling process.

A further object of the present invention is to provide a method for manufacturing a magnetic recording medium in which the coating step and the alignment step are separated.

It is further an object of the present invention to select a binder having a suitable melting point so that it can melt after the coating has been deposited while being placed in a magnetic field that causes particle orientation. This orientation is then frozen when the temperature is lowered below the melting point of the binder.

It is a further object of the present invention to provide an encapsulated ferromagnetic material in which the encapsulating binder contains a composition for imparting functional sites thereto.

It is further an object of the present invention to select an encapsulating binder material that can be electron beam cured or thermally cured to produce a hard surface that can withstand wear caused by passing recording heads over it. It is to be.

It is further an object of the present invention to orient the acicular magnetic particles in a molten binder using an electric field or a magnetic field gradient or both and a uniform magnetic field perpendicular to the surface and to cause the particles to The purpose is to provide a method for taking an appropriate position.

Other objects of the invention will become apparent from the description below.

To explain Fig. 1, Carnauba wax 842, A
-C540 (trademark of Allied Chemical Company for ethylene-acrylic acid copolymer) 42t, and gamma ferric oxide [Fe2O3, sold by Pfizer under the trade name Pferox] 392F
is charged into a two-roll rubber mill known in the industry. Additionally, A-C201 (trademark of Allied Chemical Company for calcium salt of ethylene-acrylic acid copolymer) 421 is also added. A-C540 and A-C201 act as charge directing agents, creating functional sites or hooks for which the charge directing agents can react. Another additive for adjusting functional sites is stearic acid. A-C540
can itself act as a binding agent. Other additives for controlling functional sites are styrene-acrylate copolymers, ethylene-vinyl acetate-acrylic acid plus copolymers polyethylene oxide, acrylic ester polymers, acrylic ester-acrylic acid copolymers, styrene-allyl alcohol copolymers, polyethylene oxide polymers, and a propylene-ethylene oxide copolymer. These polymers are added to adjust the functionality of the binder, but they can also act as binders themselves. Carnauba wax is particularly useful because it acts as a lubricant after the recording medium is formed. Additionally, all materials charged in the first step of the process are insoluble or non-solvable in Isopar at temperatures below 40°C. magnetic pigments, binders,
The functional site modifier is mixed in a rubber mill for 60'C11 hours, during which time the pigment is uniformly dispersed. The pigment and binder were also mixed at 130° C. using a rubber mill. High temperatures reduce pigment dispersion time.

Upon cooling, the encapsulated magnetic particles become a crayon-like solid, which is then ground. Next, the powder from the grinding process and Inverru H2100F are fed to a wet grinding process. This step takes place in a mill. Although the milling process reduces the time required for wet milling of the powder, the crayon-like solids from the rubber mill can be broken down into small particles by any means that can be shaped to conveniently load them into the mill. It is understandable that it can be done.

The encapsulated magnetic particles are then wet milled for 5 hours.

Increasing the milling time improves dispersion and reduces the average particle size. The powder fed to the wet milling process consists of spheres containing encapsulated magnetic particles. Either Pferox 4230 or Pferox 2238c can be used. These have a diameter of about 0.03~
It is 0.04 micron and has an aspect ratio of 1:6 to 1 near. A number of these acicular or dendritic magnetic particles are present within each sphere. It will be appreciated that any suitable ferromagnetic material may be used.

The non-polar liquid dispersion medium used in wet milling is an isomerized aliphatic hydrocarbon, especially Invarru 0, Invarru H,
Inverru to 1 Isopar-L and Inverru M
It is. These Impals are narrow fractions of very pure isoparaffinic hydrocarbons. For example, the boiling point range of Isopar-0 is 156-176°C. The middle boiling point of Isopar-L is about 194°C. Inverloo M
has a flash point of 77"C and a spontaneous ignition temperature of 338°C. Manufacturing standards are strict, such as limiting sulfur, acids, carboxyl, and chloride to a few ppm. They are virtually odorless and extremely light. It has only a paraffin odor and has excellent odor stability.All products are manufactured by Exxon.

All liquid dispersion media have a volumetric electrical resistance of 10 ohm-cm or more, a dielectric constant of 3.0 or less, and a vapor pressure of 10 hPa or less at 25°C. Desired Inverloo Inverloo has a flash point of ω° C. as measured by the tag closed test method. Inverru L has a flash point of 61° C. measured by the same method, and Isopar-M has a flash point of 77° C. measured by the Pensky Martens method. Although preferred dispersion media have been described above, the essentially important properties are volume resistivity and dielectric constant. Other characteristics of the dispersion medium are AS
Low kauributanol number around 27 or 28 as measured by TMD 1133.

The added additives not only serve to adjust the functional sites, but also increase the melt viscosity of the carnauba wax. Additionally, these materials can be crosslinked to harden the deposit into a hard, durable surface. The material discharged from the wet milling process is a liquid concentrate with a solids-to-dispersion ratio of approximately 40 inches. This concentrate is then diluted in Inverlu to a solids to dispersion medium ratio of approximately 20%. This dispersion is stored for future use. If this solution is to be used to deposit a magnetic coating on a substrate for use as a recording medium, the storage dispersion is diluted with Imphal to give a solids content of about 2 g.

Although examples have been given in which the charge directing agent is added in the dry milling and dilution steps, it should be understood that the charge directing agent can be added in the wet milling step if desired. There are two distinctly different types of charge directing agents. In the first case, the charge directing agent in Imphal has a higher conductivity measured at I KHz than its conductivity when mixed with toner particles.

lecithin and barium petroleum) (BaPet)
is an example of this. In the second case, the charge director in Imphal has little electrical conductivity. However, when mixed with toner particles, it exhibits a certain amount of conductivity. Barium sulfosuccinate (BaOT) and bistridecyl sulfosuccinate salts are examples in this case.

Preferred charge directing agents are those that are not electrically conductive in the absence of toner particles. Any excess conductivity is caused by the presence of ions of the same sign as the toner particles present in the bath. These unwanted ions react to the same electromagnetic field that moves the toner, depositing a non-pigmented charge.

The charge of the toner particles (0.5 to 3.0 microns radially) was measured to be in the range of 100 to several hundred. The zeta potential resulting from these charges is on the order of 1 volt, which is large compared to the thermal energy. This is made possible by the high concentration of functional moieties on each toner particle (approximately 10 to 10 moieties) and the nature of the chemical reaction between them and the charge director molecules.

A large charge on the toner particles stabilizes the dispersion.

When the spacing between particles is large, the repulsive forces between like charged particles keep the particles apart, and the long molecules act as a buffer (creating steric hindrance), causing the surfaces of the toner particles to form induced dipoles. This prevents them from coming close enough to cause agglomeration due to the effective child-attraction interaction. Coulomb mutual repulsion is inversely proportional to the distance between particles, and charge-induced dipole-attractive interaction is inversely proportional to the fourth power of the distance. As long as the particles are sufficiently separated, the dispersion, which is mainly based on mutual repulsion, is stable. If the particles are allowed to start agglomerating, their capacitance will change, the charge on the particles will change, and the properties of the bath will deteriorate.

Although the charge directing agent is added in the encapsulation step, additional charge directing agents can be added to the dispersion during the wet milling step or in the deposition step. Addition of charge directing agents during wet milling tends to improve dispersion. If the amount of charge directing agent is ideal, there will be as many negatively charged bodies as there are pigment particles. That is, there will be no excess free negatively charged ions. When the number of negative ions is excessive, the conductivity of the liquid increases, and continuous sliding conductivity is added to the developing liquid. There is one more condition that determines the upper limit of the amount of charge directing agent used. The mobility of the counterion must be greater than that of the toner particles. In this case, when an external electric field is applied that is intended to drive the toner particles toward the substrate, the more mobile counterions respond first, leaving a space charge depleted layer adjacent to the deposited substrate on the counter electrode. accumulate. The thickness of the depletion layer varies depending on the applied voltage and carrier concentration. Once the depletion layer is created, it is the only region where there is an electric field to drive the toner particles onto the substrate. In that case, the toner particles are
transfer to the substrate surface under conditions of "current limited by the inter-charge". This state is preferable because the spatial distribution of particles arriving at the surface is more uniform than a random particle distribution. The resulting film is easily uniform, smooth, and free of pinholes.

If the amount of charge directing agent is too large and the mobility of the toner particles is greater than that of the counterion, no deposition will occur under space charge limited current conditions.

The deposition step is carried out in a bath containing about 2% by weight of encapsulated charge oriented magnetic particles. The particle size distribution of the coated magnetic particles can vary. However, the mobilities of small and large particles are the same if the hook concentration is independent of particle size. Large particles accumulate a lot of charge, but small particles also have a large viscous drag. On the other hand, small particles have less charge, but have less viscous drag when moving through the liquid dispersion medium. As a result, the particle size itself acts compensatingly. The drift velocity of a particle is a function of the applied electric field); the stronger the field, the greater the drift velocity. By varying the applied field voltage, the thickness of the deposited layer can be adjusted.

For example, when depositing on a metal disk, a voltage of 400 to 100V can be used with the metal connected to the anode. The time applied to the electric field can be varied between o, ooi and 1 second. If you want to deposit onto an insulating carrier such as mylar tape, apply the anode to the back of the tape and
Apply a voltage of 00 to 5 ooo v. Again, the thickness of the deposit is controlled by the time the carrier is in the electric field. Alternatively, deposition on tape or other insulating material may be
It is also possible to first subject the substrate to a corona discharge step and then pass the charged medium through a spreading zone to deposit the toner thereon.

After completion of electrophoresis, the surface of the coated support is wetted with a bath. The bath contains undeposited particles and it is undesirable to leave them on the surface of the medium.

This surface is therefore cleaned by known methods, for example by wiper blades, doctor blades, air knives, squeegee coronas and cleaning rollers (reverse rollers, etc.), leaving a thin layer of liquid on the surface of the newly deposited magnetic layer.

It will be appreciated that all of the binders and additives soften at temperatures below 140°C. For example A-C540
softens at 108°C and has a Brookfield viscosity of 500 cps at 140°C. In order to avoid that the carrier carrying the deposited coating exhibits a dry, muddy crimp pattern, it is important to subject it to an orientation step before drying. In order to obtain a deposit without creases, the surface of the deposit must be moist before the heating in the orientation step is started. The magnetic pigment particles do not undergo any particular orientation during heating. The orientation of the magnetic particles can be adjusted both longitudinally and substantially vertically. Perpendicular magnetic recording is preferred because it allows for high density packing.

In the case of vertically oriented grains, the transition between regions of increasing and decreasing magnetization strength can be very sharp since the density of vertically oriented grains is high and there is no problem with demagnetization even in relatively thick media. However, many commercially available records and the reading heads for these records require longitudinal orientation.

Example 1 The operation described above with respect to FIG.
30 392 f, carnauba wax 849. A-C
54042f, calcium hydroxide (Ca(OH)2)
A-C5404 partially neutralized with 1,56 f.
2f, and Inverloo H2100f.

Example 2 A-C54042f as magnesium oxide (MgO) 1
．． The procedure was as in Example 1 except for partial neutralization with 39F.

Example 3 A rubber mill was fed with A-C540168F and operated as in Example 2 except that carnauba wax was not used.

Furthermore, Pferrox 2228 HC329f k was used.

Example 4 Pferrox 2228 HC392r, Carnauba Wax 135 P, A-C54066f, and A-C2
0166F was placed in a rubber mill and mixed at 130°C.

Small crayon-like pieces were taken out of the rubber mill and pulverized using a pulverizer. This powder was then fed into a wet milling process.

Inverru H2500F was added to this step.

The mill was operated for 5 hours to obtain a suspension. A portion of the suspension was diluted with 10 times by weight Inverlu H and sent to the deposition step. A number of baths were prepared with different concentrations ranging from 5% to 0.3% solids by weight. The amount of deposition on the metal disk was determined by weighing the disk before and after electrophoresis. The weight of the sediment was found to vary as a function of solids concentration.

Example 5 The operation was as in Example 4 except that the attritor was operated for 24 hours. The charge director was ditridecyl sulfosuccinate barium salt 8.41.

The deposition step was performed by depositing charged particles onto the substrate by applying a voltage, as described above. The coating thickness varies not only as a function of solids concentration in the bath, but also as a function of voltage and time. By allowing the deposition to proceed for a sufficient period of time, the bath of magnetic particles between the developing electrode and the circular substrate can be completely depleted.

The time for applying the operating voltage can be varied from 0.1 seconds to more than 2 seconds.

Deposition onto the substrate was carried out by different methods. Second
Referring to the figure, the developing electrodes 2 are placed parallel to the base 4 at an interval of 0.1 to 5 m+. The interval is usually IM. The assembly is then inserted into the toner bath 6 in the container 3, the switch 5 is closed and a voltage pulse from the voltage source 8 is applied for a predetermined period of time. The assembly is then removed from the bath, the deploying electrode is separated from the substrate, and the excess liquid is removed by immersing the substrate in pure Imphal and rotating it, and an air knife (not shown) is used to clean the surface. Pass and remove. Next, move the base f while it is still wet to the heater (
(not shown) and the temperature is raised to the melting point of the binder. This heating step is carried out while subjecting the part to a uniform magnetic field. Then, while the part is still held in the magnetic field, the temperature is lowered below the melting point to solidify the binder.

In this way the orientation of the magnetic particles is fixed in the hardened solid. To achieve the required circumferential longitudinal orientation of a hard or floppy disk, known orientation methods are carried out while the disk is heated above the melting point of the binder. Vertical orientation is achieved by placing the substrate parallel to the pole pieces of the C-type magnet during the heating cycle.

Next, referring to FIG. 3, deposition was carried out on a metal disk placed on a movable table 12. The assembly is typically submerged in a toner bath 6) and withdrawn from the bath at a uniform rate of 1 to 10 inches/second. A voltage is applied between the developing electrode 14 and the base disk 10 as shown in FIG.

Excess toner is removed by a conventional reverse roller 16, and the disk 10 is then subjected to the heating and orientation steps described above.

FIG. 4 is a diagram showing one configuration of an apparatus for preparing deposits on a continuous tape. The wound tape 20 is passed around a grounded metal drum 22 and wound around a roller 24.

The portion of the tape 21 passing between the ground drum 22 and the bearing roller 24 is previously subjected to the action of the corona 26, and passes between the expanding electrode 28 and the ground metal drum n. By pumping the toner liquid from the toner bath 32 to the recessed electrode 2
The toner is sent to the toner reservoir 34 in 8. The bath products from Tamaokara return to the toner bath 32. Although metal roller 22 is shown as being grounded, it may be insulated from ground and energized if desired.

The freshly coated web portion 21 passes between suitable heating elements ω to soften the polymer or binder present in the toner. The term "toner" herein is to be understood as referring to a developing liquid containing dispersed therein a binder, magnetic particles, a diluent such as one of the Imphals, and a charge directing agent. Unless otherwise specified, the toner bath is prepared according to the first four steps of FIG.

The present disclosure was primarily directed to acicular magnetic particles. However, although acicular magnetic particles with a vertical or longitudinal orientation are preferred, it should be understood that the present invention may be applied to any desired form of ferromagnetic or iron-containing particles.

The binder and magnetic particles are deposited onto the web by electrophoresis. The web containing the softened binder is passed through the magnetic field created by the magnet. South pole 4 of this magnet
2 and the arctic drama are diagrammatically shown in Figure 4. The magnetic particles are oriented in a desired direction depending on the magnetic flux and the direction of the magnetic field. The speed of passage of the web portion 21 and the length of the magnetic field are such that the temperature of the coated web falls below the curing temperature of the binder before it leaves the magnetic field. The web then passes through an electron beam curing zone, shown diagrammatically at 46 in the figure.

It is well known in the industry that vertical alignment occurs in acicular magnetic particles when the magnetic field direction is proper. Magnetic particles deposited by conventional spin or electrophoretic deposition methods are usually randomly distributed and randomly oriented. The effect of the magnetic field exerts a torque on the particles, which orients them collinear with the lines of applied magnetic flux. Since the particle centers are initially randomly distributed, after orientation the particle heads will be located at random distances from the surface of the web.

Due to interactions between particles, the root mean square distance between the surface of the web coating and the particle heads tends to increase.

This phenomenon causes noise during recording. A magnified view of particles oriented by a perpendicular magnetic field shows this change in distance of adjacent particles from the upper surface of the web coating.

This situation is similar to the skyline created by New York's tall buildings.

This is therefore called the "Manhattan Vista" effect. During the orientation process in a magnetic field, this Manhattan Vista effect, in addition to the torque produced by the uniform magnetic field, moves the center of mass of the particles so that all particle heads are essentially equidistant from the web-coated surface. This can be prevented by applying such a force to the particles.

FIG. 5 shows a method for reducing the Manhattan Vista effect. The disk shown in the figure is similar to the disk 10 shown in FIG. The disc is newly coated with a film 52 containing magnetic particles and is in a softened state after receiving thermal energy. A voltage is applied between the discs and the metal part 54. Part 54 is an electrically conductive but non-magnetic material;
I have 56 naifetsuji. Disk 50 and metal parts 5
When a voltage is applied from a voltage source 60 between the film 52 and the
An electric field gradient is applied to the 0 surface. Since the dielectric constant of the magnetic particles is greater than that of the film's binder, a net force is exerted on the magnetic particles that moves the particles toward the film surface relative to the binder. Electric field gradients also tend to slightly disturb particle orientation. However, there is also an orientation parallel to the lines of magnetic flux of a uniform magnetic field. Similar results were obtained by using a wedge made of magnetic material with a sharp edge in place of the knife wedge shown in FIG.

As mentioned above, the direction of the magnetic field determines whether the magnetic particles are arranged vertically or horizontally. An example of a vertical or horizontal orientation is shown in FIG. 6, and an example of a perpendicular or vertical orientation is shown in FIG. These micrographs were taken with a scanning electron microscope at a magnification of 22 and 500 times. The horizontal bar is 1
Represents the scale of microns. The electron beam energy used was 20 KV.

The photograph was taken straight down on the top surface of the sample.

This is indicated by "00" on the micrograph. "S" indicates that the electron beam microscope was operated in the secondary electron collection mode. This orientation step also has the advantage that the magnet removes all visible solids from the bath.

Since the final product of the method of the invention is a magnetic recording tape, floppy disk, or hard disk, it is desirable that the coating include a lubricant. Carnauba wax is an excellent lubricant. When stearic acid is used to create the ionic sites, it also acts as a lubricant.

Vertical orientation of toner particles provides high density recording.

This can be obtained not only by acicular magnetic particles but also by barium ferrous oxide platelets (BaFe□2019). Other forms of magnetic particles may be used as well. Those skilled in the art will appreciate that the design of the read/write head must be matched to the configuration and orientation of the recording medium.

In the orientation step, the polymer is heated to its melting point so that the magnetic particles can be oriented under the influence of a magnetic field.

This does not allow for particle orientation and tends to align the particles against the surface of the coating.

After the orientation step, the coating is cured. A-0540 binder is easily cured by electron beam. Any suitable curing method can be used depending on the nature of the binder.

It will be appreciated that the various compositions of the Examples described above were subjected to the steps shown in FIG. 1 with excellent results.

Example 6 The same procedure as Example 4 was carried out except that acryloid DM-5466f was used in place of A-C201. This is an acrylic resin manufactured by Rohm and Haas that acts as a charge director.

Example 7 Pferotux 2228 I(C (Pfizer product)
392f, Carnauba wax 842, A-C54084F
The procedure was the same as described for FIG. 1, except that . Furthermore, sulfosuccinic acid ditridecyl barium salt 9?
was added in the dry milling process as a charge director. The operation shown in FIG. 1 was continued up to the dilution step to obtain a toner bath having a solid content of 1.5 inches. Toner particles are approximately 1 micron in diameter.
It consisted of several unoriented ferrous oxide particles encapsulated in a binder. This toner bath was then used to electrophoretically deposit a thin layer of magnetic particles onto an aluminum substrate. The electrophoretic deposition process proceeds very quickly. Accordingly, 1. the method of the present invention can be used to deposit magnetic coatings onto webs moving at high speeds.

The prior art does not disclose the encapsulation of magnetic iron-containing or ferromagnetic particles.

Functionality can be imparted or controlled by dry milling in the presence of charge directing agents.

To prepare a developer for a photocopy machine, the process steps of comminution, wet milling, and dilution of the wet milled paste are followed.

Through the above, the objects of the present invention have been achieved. The present inventors have provided a method for manufacturing magnetic recording media by electrophoretic deposition, in which the thickness of the deposited layer can be easily adjusted. The method of the invention makes it possible to produce magnetic recording coatings on carriers that are uniform in thickness and are substantially free of pinholes. The magnetic recording manufacturing method of the present invention can be carried out quickly and continuously and is therefore particularly suitable for use in mass production. The present invention provides suspensions useful in practicing the methods of the present invention that can encapsulate acicular ferromagnetic particles and thereby reduce breakage of these particles during the milling process. According to the method of the present invention, a magnetic recording medium can be manufactured by separating the coating step and the orientation step so that any desired orientation can be given to the magnetic particles. Compositions useful in practicing the methods of the invention include an encapsulating binder suitable for encapsulating magnetic particles or other particles together with a means for imparting a functional moiety to the encapsulating binder. provided. These functional sites can impart a desired polar charge to the binder, thereby adjusting the electrophoretic deposition rate of the coating for a given applied voltage.

It will be appreciated that certain useful features and subcombinations may be used independently of other features and subcombinations. This is contemplated and falls within the scope of the claims of the present invention. Furthermore, it is clear that various changes in detail may be made within the scope of the claims without departing from the spirit of the invention. It is therefore to be understood that the invention is not limited to the specific details described and described.

[Brief explanation of drawings]

The accompanying drawings constitute a part of this specification, and should be understood in connection with this specification. In the figures, the same reference numerals are used to indicate similar parts in each figure. FIG. 1 is a flow sheet showing the steps of a method for carrying out the invention. FIG. 2 is a diagram illustrating one of the apparatuses for depositing magnetic particles onto a substrate. FIG. 3 is a diagram showing another apparatus for depositing magnetic particles onto a substrate. FIG. 4 is a diagram showing an apparatus for depositing magnetic particles onto a continuous web. FIG. 5 is a diagram illustrating another apparatus for depositing magnetic particles that prevents the "Manhattan Vista" effect. FIG. 6 is a scanning electron micrograph of longitudinally oriented magnetic particles magnified 22,500 times. FIG. 7 is a scanning electron micrograph of the same orthogonally oriented magnetic particles as in FIG. 6, magnified 22,500 times. FIG, 1 Fl [1,4 ° (Mumu procedural amendment (method) June 20, 1986

Claims (18)

[Claims] (1) Dry milling a large amount of magnetic particles with a small amount of a binder and a small amount of a charge directing agent to produce solid pieces of encapsulated magnetic particles; pulverizing the pieces into fine pieces; Wet-milling a small amount of said particles with a large amount of a low-boiling aliphatic hydrocarbon liquid to produce a suspension, and electrophoretically depositing encapsulated magnetic particles on a carrier medium from said suspension. a step, orienting the magnetic particles;
and then curing the binder to produce a magnetic recording medium. (2) The method according to item (1) above, wherein the additional charge-directing agent is added in a step prior to the deposition step. (3) The method according to item (2) above, wherein an additional charge directing agent is added in the wet milling step. (4) a large amount of iron-containing particles with a small amount of binder and a small amount of
dry milling with a charge-directing agent suitable for functional site generation to form solid pellets of encapsulated iron-containing particles; pulverizing the pellets in a milling step; wet milling with a boiling point aliphatic hydrocarbon liquid and a charge-directing agent to produce a suspension; electrophoretically depositing encapsulated iron-containing particles from said suspension on a carrier medium; Production of a composition suitable for electrophoretically depositing a magnetic coating onto a carrier medium, characterized in that it comprises the steps of orienting the particles contained therein and then curing the binder to produce a magnetic recording medium. Method. (5) The carrier medium is metal, and the thickness of the deposited layer in the electrophoretic deposition step is adjusted by applying a voltage of 400 V to 1000 V for 0.001 seconds to 1 second. Method. (6) The method according to item (4), wherein the pulverization step forms a powder with an average particle size of 200 microns. (7) The wet milling step is carried out using sufficient low-boiling aliphatic hydrocarbon liquid to have a solids content of 40%;
The method described in 4). (8) The method according to item (4), wherein the suspension is diluted to a solids content of 20% to enable storage of the composition. (9) The method according to item (4), wherein the suspension is diluted to a solids content of 1 to 59% before carrying out the precipitation step. (10) The carrier medium is an insulating material, and the voltage applied during the electrophoretic deposition step is between 2000V and 5000V.
The method described in the preceding paragraph (4), which is (11) The method according to item (4), wherein the plurality of magnetic particles are present in powder form during the pulverization step. (12) comprising a plurality of magnetic particles encapsulated in a binder, said binder comprising a thermoplastic polymer, said polymer being insoluble in a low boiling hydrocarbon liquid at ambient or room temperature; A composition that can be softened at a temperature of 70°C or higher. (13) Electrophoretic deposition of magnetic particles onto a carrier, comprising a small amount of the composition described in the preceding paragraph (12), a small amount of a charge directing agent, and a large amount of a low-boiling aliphatic hydrocarbon liquid. Suspension for possible. (14) The composition according to the above item (12), which contains a small amount of an auxiliary agent suitable for dispersing and producing functional moieties in the binder. (15) comprising a carrier and a coating of magnetic particles deposited thereon, wherein the magnetic particles are insoluble in a low boiling aliphatic hydrocarbon liquid at ambient or room temperature and 70°C.
encapsulated in a binder comprising a thermoplastic polymer capable of softening at temperatures above, said binder having a plurality of functional sites and mixed with a small amount of a charge directing agent; A magnetic recording medium, wherein the magnetic particles have substantially the same orientation. (16) Dry milling a large amount of ferromagnetic particles with a small amount of a binder and a small amount of a charge directing agent to produce solid pieces of encapsulated ferromagnetic particles, wherein the encapsulant has functional moieties. The ferromagnetic material is electrophoretically deposited onto a carrier by grinding the particles into fine pieces and wet-milling the fine pieces with a large amount of a low-boiling aliphatic hydrocarbon liquid. A method for producing a composition suitable for electrophoretically depositing ferromagnetic particles onto a carrier, the method comprising the step of producing a suspension obtained by electrophoretically depositing ferromagnetic particles onto a carrier. (17) The method according to item (16), wherein an additional charge directing agent is added to the suspension. (18) The method according to item (16), wherein the ferromagnetic material contains a thin layer of iron-containing particles.